OXIDATION PROCESSES IN THE SOIL 521 



the action of the sulfhydryl group; 3 (3) by substances which are capable 

 of peroxide formation. 4 



The oxygen liberated in synthetic processes is consumed directly for 

 the liberation of energy as in the formation of amino acids from organic 

 acids and ammonia, which is the first step in protein synthesis by 

 heterotrophic microorganisms : 



2 CH 3 • CO • COOH + 2 NH 3 = 2 CH 3 • CH • NH 2 ■ COOH + O, 



1/6 (C 6 H 12 6 ) + O2 -» C0 2 + H 2 



The oxygen in the C0 2 molecule that has thus become liberated is 

 not derived from free gas but from a molecule capable of reduction 

 by glucose, a phenomenon distinctly different from that involving 

 oxygen occurring in an external medium. 5 In considering oxidation as 

 the activation of hydrogen, atomic oxygen will be formed if the hydrogen 

 of water is activated. In the presence of a substance, such as methyl- 

 ene blue or nitrates, which readily absorbs hydrogen, oxidation be- 

 comes possible as a result of the reduction of the active hydrogen. For 

 example, acetic acid bacteria oxidize alcohol in the absence of oxygen 

 but in the presence of methylene blue. 



CH, CH 2 OH = CH 3 COH + 2 H + 

 2H+ + O ->■ HjO 



The role of oxygen consists in binding the hydrogen and its place can 

 be taken by other hydrogen acceptors. The acetaldehyde is changed 

 by the Cannizzaro reaction to alcohol and acetic acid, this process 

 being accompanied by the liberation of energy: 



2 CH 3 COH + H 2 -* CH 3 • COOH + CH 3 • CH 2 OH 



The phenomena of oxidation and reduction by microorganisms are 

 brought about in most instances by means of specific enzymes of the 

 oxidase-peroxidase nature on the one hand and reductase or perhydridase 

 nature on the other. 

 The oxidation-reduction intensities of biological systems can be 



3 Hopkins. Biochem. Jour., 19: 798. 1925. 



4 See Quastel, J. H. Dehydrogenations produced by resting bacteria. IV. 

 A theory of the mechanism of oxidations and reductions in vivo. Biochem. 

 Jour., 20: 166-194. 1926. 



* Aubel, E., and Wurmser, R. Sur l'utilisation de l'Snergie Iib6r6e par les 

 oxydations. Compt. Rend. Acad. Sci., 179: 848-851. 1924. 



